MacBook Air face-off: HDD vs SSD (with video)

In this fourth installment of our MacBook Air review series, we pit Apple's standard hard disk drive (HDD) model against the standard solid state drive (SSD) configuration in a set of battery and benchmark tests to gauge the performance and power saving capabilities of each. Videos are used to demonstrate a side-by-side simultaneous boot, as well some application launch tests.

Most critics of the MacBook Air have largely focused on what it doesn't have in comparison to the full size MacBook and high end MacBook Pro. This sounds a lot like complaining that a convertible lacks seats for six adults and the cargo room of a minivan. What's more interesting about the Air is how well it serves the purpose it was intended to achieve: a light, thin, and highly mobile laptop.

The previous two segments looked at issues faced by early adopters. Early adopter issues: MacBook Air and Migration Assistant examined the problems related to using only its built in WIFI 802.11n wireless networking to import files and users from another computer. In initial testing, it looked like the problem was the speed limitations of WiFi, but our followup testing suggests that WiFi can be very competitive for installing software.

In addition to the customary features Apple pared away from the Air to make it lighter, thinner, and less expensive, the new laptop also offers a new option: a solid state drive. It's not cheap, but it is fast and promises to be more reliable than a physical hard drive mechanism. SSDs use high density Flash RAM chips to store data in place of a conventional HDD's magnetically read platters.

The New SSD: More Expensive, Less Storage

Solid state drives are expensive, but costs are coming down. Of course, there's still a long way for their price tags to go. A 1.8" 64 GB SSD costs around $1600 at retail and 128GB versions are $3000 and up. The only thing that will force these prices down is the economies of scale from widespread adoption. A number of specialized ultra mobile laptops began offering an SSD option over the last six months, but Apple's more mainstream offering in the MacBook Air presents high capacity SSDs to a wide new audience. The One Laptop Per Child XO and Asus Eee PC also use SSD, but in much smaller sizes ranging from 1GB on the XO and between 2 and 8GB SSDs on the Eee PC.

An SSD is more than just Flash RAM chips; it also includes an ATA interface so the memory chips appear to the computer just like a hard drive. The iPhone and Flash iPods use Flash RAM, but not packaged in an SSD nor using an ATA interface. The SSD is designed as a package to be functionally identical to a standard hard drive and act as a drop-in replacement. That means Air users who opt for the standard HDD will be able to upgrade themselves to an SSD in the future using an off the shelf SSD that will likely be both larger and cheaper than what is available today. The high cost of SSD effectively limits its practical use to ultra mobile laptops and other specialty devices, where its advantages in speed, power savings, and reliability can offset its current price and capacity limitations.

Upgrading from the Air's standard 80GB HDD to a 64GB SSD costs a steep $999. The biggest downside after cost is the drop in capacity. Formatted, the 64GB SSD has a capacity of 55.6GB. With the default software install, its ships with around 38 GB available. As Bare Feats notes, "If we reserve 8GB for Virtual Memory, that only leaves us 30GB for documents, tunes, movies, photos, and third party apps." Users who need more than that will have to stick with the standard conventional hard drive. In comparison, the 80GB HDD supplies 74.5GB formatted capacity, and with the pre-installed software offers roughly 55GB available to the user.

SSD Speed Advantage

Fortunately, the SSD offers some advantages as well; the most obvious is speed. Flash RAM data writing usually isn't actually faster than a conventional hard drive; in sequential write tests the SSD was only 60-80% as fast. However, in disk reading and particularly random access reads, the SSD was dramatically faster: as much as 18 times faster.

That means faster booting, faster application launching, and faster open file operations, all tasks where the user is likely be waiting for disk access to finish. Write speeds during file saving have less of an impact on usability. In general file operations and copying, the weakness of SSD to write is well overshadowed by its blazing ability to read and its special prowess at randomly reading information on disk. A mechanical HDD has to physically move its head across the disk to perform random access operations.

SSD read speeds won't make the overall system dramatically faster all the time, but they are noticeable any time a lot of data is being read. Boot times were consistently much faster. As the video (below) demonstrates, the SSD was able to finish booting and connect to a wireless network while the HDD model was still spinning its gear on the grey boot screen.

We also selected 17 applications to simultaneously launch (excluding any that obscure the display such as Front Row). The SSD was able to rapidly load all of them at once, while the HDD struggled to manage so much concurrent disk activity. By the time it had finished, the SSD model had already put the display to sleep (below).

However, the speed launch trick is only impressive at the first launch of an application after a reboot. Mac OS X aggressively caches data to allow the slower HDD launch its applications nearly as fast on a second try (below).

As Flash prices drop, the performance advantage of SSD will begin to outweigh the cost, and current capacity limitations promise to be less of a factor as well. That will allow Apple to focus its Mac OS X development efforts on optimal SSD reading and cached writing, rather than catering its optimizations to the nature of standard hard drives with longer latency and seek times.